feat(cdk-experimental/tabs): support initial tab selection and add unit tests

src/cdk-experimental/tabs/tabs.ts

@@ -20,7 +20,7 @@ import {
   inject,
   input,
   model,
-  signal,
+  linkedSignal,
 } from '@angular/core';
 import {toSignal} from '@angular/core/rxjs-interop';
 import {TabListPattern, TabPanelPattern, TabPattern} from '../ui-patterns';
@@ -97,6 +97,9 @@ export class CdkTabList {
   /** The CdkTabs nested inside of the CdkTabList. */
   private readonly _cdkTabs = contentChildren(CdkTab);
 
+  /** The internal tab selection state. */
+  private readonly _selection = linkedSignal(() => (this.tab() ? [this.tab()!] : []));
+
   /** A signal wrapper for directionality. */
   protected textDirection = toSignal(this._directionality.change, {
     initialValue: this._directionality.value,
@@ -126,13 +129,21 @@ export class CdkTabList {
   /** The current index that has been navigated to. */
   activeIndex = model<number>(0);
 
+  // TODO(ok7sai): Provides a default state when there is no pre-select tab.
+  /** The current selected tab. */
+  tab = model<string | undefined>();
+
   /** The TabList UIPattern. */
   pattern: TabListPattern = new TabListPattern({
     ...this,
     items: this.tabs,
     textDirection: this.textDirection,
-    value: signal<string[]>([]),
+    value: this._selection,
   });
+
+  constructor() {
+    effect(() => this.tab.set(this._selection()[0]));
+  }
 }
 
 /** A selectable tab in a TabList. */

src/cdk-experimental/ui-patterns/tabs/BUILD.bazel

@@ -1,4 +1,4 @@
-load("//tools:defaults.bzl", "ts_project")
+load("//tools:defaults.bzl", "ng_web_test_suite", "ts_project")
 
 package(default_visibility = ["//visibility:public"])
 
@@ -17,3 +17,22 @@ ts_project(
         "//src/cdk-experimental/ui-patterns/behaviors/signal-like",
     ],
 )
+
+ts_project(
+    name = "unit_test_sources",
+    testonly = True,
+    srcs = [
+        "tabs.spec.ts",
+    ],
+    deps = [
+        ":tabs",
+        "//:node_modules/@angular/core",
+        "//src/cdk/keycodes",
+        "//src/cdk/testing/private",
+    ],
+)
+
+ng_web_test_suite(
+    name = "unit_tests",
+    deps = [":unit_test_sources"],
+)

src/cdk-experimental/ui-patterns/tabs/tabs.spec.ts

@@ -0,0 +1,304 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.dev/license
+ */
+
+import {signal} from '@angular/core';
+import {
+  TabInputs,
+  TabPattern,
+  TabListInputs,
+  TabListPattern,
+  TabPanelInputs,
+  TabPanelPattern,
+} from './tabs';
+import {SignalLike, WritableSignalLike} from '../behaviors/signal-like/signal-like';
+import {createKeyboardEvent} from '@angular/cdk/testing/private';
+import {ModifierKeys} from '@angular/cdk/testing';
+
+// Converts the SignalLike type to WritableSignalLike type for controlling test inputs.
+type WritableSignalOverrides<O> = {
+  [K in keyof O as O[K] extends SignalLike<any> ? K : never]: O[K] extends SignalLike<infer T>
+    ? WritableSignalLike<T>
+    : never;
+};
+
+type TestTabListInputs = TabListInputs & WritableSignalOverrides<TabListInputs>;
+type TestTabInputs = TabInputs & WritableSignalOverrides<TabInputs>;
+type TestTabPanelInputs = TabPanelInputs & WritableSignalOverrides<TabPanelInputs>;
+
+const up = (mods?: ModifierKeys) => createKeyboardEvent('keydown', 38, 'ArrowUp', mods);
+const down = (mods?: ModifierKeys) => createKeyboardEvent('keydown', 40, 'ArrowDown', mods);
+const left = (mods?: ModifierKeys) => createKeyboardEvent('keydown', 37, 'ArrowLeft', mods);
+const right = (mods?: ModifierKeys) => createKeyboardEvent('keydown', 39, 'ArrowRight', mods);
+const home = (mods?: ModifierKeys) => createKeyboardEvent('keydown', 36, 'Home', mods);
+const end = (mods?: ModifierKeys) => createKeyboardEvent('keydown', 35, 'End', mods);
+const space = (mods?: ModifierKeys) => createKeyboardEvent('keydown', 32, ' ', mods);
+const enter = (mods?: ModifierKeys) => createKeyboardEvent('keydown', 13, 'Enter', mods);
+
+function createTabElement(): HTMLElement {
+  const element = document.createElement('div');
+  element.role = 'tab';
+  return element;
+}
+
+describe('Tabs Pattern', () => {
+  let tabListInputs: TestTabListInputs;
+  let tabListPattern: TabListPattern;
+  let tabInputs: TestTabInputs[];
+  let tabPatterns: TabPattern[];
+  let tabPanelInputs: TestTabPanelInputs[];
+  let tabPanelPatterns: TabPanelPattern[];
+
+  beforeEach(() => {
+    // Initiate TabListPattern.
+    tabListInputs = {
+      orientation: signal('horizontal'),
+      wrap: signal(true),
+      textDirection: signal('ltr'),
+      selectionMode: signal('follow'),
+      focusMode: signal('roving'),
+      disabled: signal(false),
+      activeIndex: signal(0),
+      skipDisabled: signal(true),
+      items: signal([]),
+      value: signal(['tab-1']),
+    };
+    tabListPattern = new TabListPattern(tabListInputs);
+
+    // Initiate a list of TabPatterns.
+    tabInputs = [
+      {
+        tablist: signal(tabListPattern),
+        tabpanel: signal(undefined),
+        id: signal('tab-1-id'),
+        element: signal(createTabElement()),
+        disabled: signal(false),
+        value: signal('tab-1'),
+      },
+      {
+        tablist: signal(tabListPattern),
+        tabpanel: signal(undefined),
+        id: signal('tab-2-id'),
+        element: signal(createTabElement()),
+        disabled: signal(false),
+        value: signal('tab-2'),
+      },
+      {
+        tablist: signal(tabListPattern),
+        tabpanel: signal(undefined),
+        id: signal('tab-3-id'),
+        element: signal(createTabElement()),
+        disabled: signal(false),
+        value: signal('tab-3'),
+      },
+    ];
+    tabPatterns = [
+      new TabPattern(tabInputs[0]),
+      new TabPattern(tabInputs[1]),
+      new TabPattern(tabInputs[2]),
+    ];
+
+    // Initiate a list of TabPanelPatterns.
+    tabPanelInputs = [
+      {
+        id: signal('tabpanel-1-id'),
+        tab: signal(undefined),
+        value: signal('tab-1'),
+      },
+      {
+        id: signal('tabpanel-2-id'),
+        tab: signal(undefined),
+        value: signal('tab-2'),
+      },
+      {
+        id: signal('tabpanel-3-id'),
+        tab: signal(undefined),
+        value: signal('tab-3'),
+      },
+    ];
+    tabPanelPatterns = [
+      new TabPanelPattern(tabPanelInputs[0]),
+      new TabPanelPattern(tabPanelInputs[1]),
+      new TabPanelPattern(tabPanelInputs[2]),
+    ];
+
+    // Binding between tabs and tabpanels.
+    tabInputs[0].tabpanel.set(tabPanelPatterns[0]);
+    tabInputs[1].tabpanel.set(tabPanelPatterns[1]);
+    tabInputs[2].tabpanel.set(tabPanelPatterns[2]);
+    tabPanelInputs[0].tab.set(tabPatterns[0]);
+    tabPanelInputs[1].tab.set(tabPatterns[1]);
+    tabPanelInputs[2].tab.set(tabPatterns[2]);
+    tabListInputs.items.set(tabPatterns);
+  });
+
+  it('sets the selected tab by setting `value`.', () => {
+    expect(tabPatterns[0].selected()).toBeTrue();
+    expect(tabPatterns[1].selected()).toBeFalse();
+    tabListInputs.value.set(['tab-2']);
+    expect(tabPatterns[0].selected()).toBeFalse();
+    expect(tabPatterns[1].selected()).toBeTrue();
+  });
+
+  it('sets a tabpanel to be not hidden if a tab is selected.', () => {
+    tabListInputs.value.set(['tab-1']);
+    expect(tabPatterns[0].selected()).toBeTrue();
+    expect(tabPanelPatterns[0].hidden()).toBeFalse();
+  });
+
+  it('sets a tabpanel to be hidden if a tab is not selected.', () => {
+    tabListInputs.value.set(['tab-1']);
+    expect(tabPatterns[1].selected()).toBeFalse();
+    expect(tabPanelPatterns[1].hidden()).toBeTrue();
+  });
+
+  it('gets a controlled tabpanel id from a tab.', () => {
+    expect(tabPanelPatterns[0].id()).toBe('tabpanel-1-id');
+    expect(tabPatterns[0].controls()).toBe('tabpanel-1-id');
+    expect(tabPanelPatterns[1].id()).toBe('tabpanel-2-id');
+    expect(tabPatterns[1].controls()).toBe('tabpanel-2-id');
+    expect(tabPanelPatterns[2].id()).toBe('tabpanel-3-id');
+    expect(tabPatterns[2].controls()).toBe('tabpanel-3-id');
+  });
+
+  describe('Keyboard Navigation', () => {
+    it('does not handle keyboard event if a tablist is disabled.', () => {
+      expect(tabPatterns[1].active()).toBeFalse();
+      tabListInputs.disabled.set(true);
+      tabListPattern.onKeydown(right());
+      expect(tabPatterns[1].active()).toBeFalse();
+    });
+
+    it('skips the disabled tab when `skipDisabled` is set to true.', () => {
+      tabInputs[1].disabled.set(true);
+      tabListPattern.onKeydown(right());
+      expect(tabPatterns[0].active()).toBeFalse();
+      expect(tabPatterns[1].active()).toBeFalse();
+      expect(tabPatterns[2].active()).toBeTrue();
+    });
+
+    it('does not skip the disabled tab when `skipDisabled` is set to false.', () => {
+      tabListInputs.skipDisabled.set(false);
+      tabInputs[1].disabled.set(true);
+      tabListPattern.onKeydown(right());
+      expect(tabPatterns[0].active()).toBeFalse();
+      expect(tabPatterns[1].active()).toBeTrue();
+      expect(tabPatterns[2].active()).toBeFalse();
+    });
+
+    it('selects a tab by focus if `selectionMode` is "follow".', () => {
+      expect(tabPatterns[0].selected()).toBeTrue();
+      expect(tabPatterns[1].selected()).toBeFalse();
+      tabListPattern.onKeydown(right());
+      expect(tabPatterns[0].selected()).toBeFalse();
+      expect(tabPatterns[1].selected()).toBeTrue();
+    });
+
+    it('selects a tab by enter key if `selectionMode` is "explicit".', () => {
+      tabListInputs.selectionMode.set('explicit');
+      expect(tabPatterns[0].selected()).toBeTrue();
+      expect(tabPatterns[1].selected()).toBeFalse();
+      tabListPattern.onKeydown(right());
+      expect(tabPatterns[0].selected()).toBeTrue();
+      expect(tabPatterns[1].selected()).toBeFalse();
+      tabListPattern.onKeydown(enter());
+      expect(tabPatterns[0].selected()).toBeFalse();
+      expect(tabPatterns[1].selected()).toBeTrue();
+    });
+
+    it('selects a tab by space key if `selectionMode` is "explicit".', () => {
+      tabListInputs.selectionMode.set('explicit');
+      expect(tabPatterns[0].selected()).toBeTrue();
+      expect(tabPatterns[1].selected()).toBeFalse();
+      tabListPattern.onKeydown(right());
+      expect(tabPatterns[0].selected()).toBeTrue();
+      expect(tabPatterns[1].selected()).toBeFalse();
+      tabListPattern.onKeydown(space());
+      expect(tabPatterns[0].selected()).toBeFalse();
+      expect(tabPatterns[1].selected()).toBeTrue();
+    });
+
+    it('uses left key to navigate to the previous tab when `orientation` is set to "horizontal".', () => {
+      tabListInputs.activeIndex.set(1);
+      expect(tabPatterns[1].active()).toBeTrue();
+      tabListPattern.onKeydown(left());
+      expect(tabPatterns[0].active()).toBeTrue();
+    });
+
+    it('uses right key to navigate to the next tab when `orientation` is set to "horizontal".', () => {
+      tabListInputs.activeIndex.set(1);
+      expect(tabPatterns[1].active()).toBeTrue();
+      tabListPattern.onKeydown(right());
+      expect(tabPatterns[2].active()).toBeTrue();
+    });
+
+    it('uses up key to navigate to the previous tab when `orientation` is set to "vertical".', () => {
+      tabListInputs.orientation.set('vertical');
+      tabListInputs.activeIndex.set(1);
+      expect(tabPatterns[1].active()).toBeTrue();
+      tabListPattern.onKeydown(up());
+      expect(tabPatterns[0].active()).toBeTrue();
+    });
+
+    it('uses down key to navigate to the next tab when `orientation` is set to "vertical".', () => {
+      tabListInputs.orientation.set('vertical');
+      tabListInputs.activeIndex.set(1);
+      expect(tabPatterns[1].active()).toBeTrue();
+      tabListPattern.onKeydown(down());
+      expect(tabPatterns[2].active()).toBeTrue();
+    });
+
+    it('uses home key to navigate to the first tab.', () => {
+      tabListInputs.activeIndex.set(1);
+      expect(tabPatterns[1].active()).toBeTrue();
+      tabListPattern.onKeydown(home());
+      expect(tabPatterns[0].active()).toBeTrue();
+    });
+
+    it('uses end key to navigate to the last tab.', () => {
+      tabListInputs.activeIndex.set(1);
+      expect(tabPatterns[1].active()).toBeTrue();
+      tabListPattern.onKeydown(end());
+      expect(tabPatterns[2].active()).toBeTrue();
+    });
+
+    it('moves to the last tab from first tab when navigating to the previous tab if `wrap` is set to true', () => {
+      expect(tabPatterns[0].active()).toBeTrue();
+      tabListPattern.onKeydown(left());
+      expect(tabPatterns[2].active()).toBeTrue();
+    });
+
+    it('moves to the first tab from last tab when navigating to the next tab if `wrap` is set to true', () => {
+      tabListPattern.onKeydown(end());
+      expect(tabPatterns[2].active()).toBeTrue();
+      tabListPattern.onKeydown(right());
+      expect(tabPatterns[0].active()).toBeTrue();
+    });
+
+    it('stays on the first tab when navigating to the previous tab if `wrap` is set to false', () => {
+      tabListInputs.wrap.set(false);
+      expect(tabPatterns[0].active()).toBeTrue();
+      tabListPattern.onKeydown(left());
+      expect(tabPatterns[0].active()).toBeTrue();
+    });
+
+    it('stays on the last tab when navigating to the next tab if `wrap` is set to false', () => {
+      tabListInputs.wrap.set(false);
+      tabListPattern.onKeydown(end());
+      expect(tabPatterns[2].active()).toBeTrue();
+      tabListPattern.onKeydown(right());
+      expect(tabPatterns[2].active()).toBeTrue();
+    });
+
+    it('changes the navigation direction with `rtl` mode.', () => {
+      tabListInputs.textDirection.set('rtl');
+      tabListInputs.activeIndex.set(1);
+      tabListPattern.onKeydown(left());
+      expect(tabPatterns[2].active()).toBeTrue();
+    });
+  });
+});

src/cdk-experimental/ui-patterns/tabs/tabs.ts

@@ -6,8 +6,7 @@
  * found in the LICENSE file at https://angular.dev/license
  */
 
-import {computed, signal} from '@angular/core';
-
+import {computed} from '@angular/core';
 import {KeyboardEventManager} from '../behaviors/event-manager/keyboard-event-manager';
 import {PointerEventManager} from '../behaviors/event-manager/pointer-event-manager';
 import {ListFocus, ListFocusInputs, ListFocusItem} from '../behaviors/list-focus/list-focus';
@@ -190,7 +189,7 @@ export class TabListPattern {
     this.navigation = new ListNavigation({...inputs, focusManager: this.focusManager});
     this.selection = new ListSelection({
       ...inputs,
-      multi: signal(false),
+      multi: () => false,
       focusManager: this.focusManager,
     });
   }